Thermally-responsive switch



Sept. 30, 1969 J- E. SHOCKROO ET AL THERMALLYFRESPONSIVE SWITCH 2 Sheets-Sheet 1 Filed Jan. 27, 1967 o 6 9 o v 0 .4 W .x \wiww w a .t e E. m! E. Ii vkLM 5m 0 E, u E M lllll r 2 WH m v am? 0 a a M/onv \XX/ Sept. 30, 1969 J s oo ET AL 3,470,513

THERMALLY-RESPONSIVE SWITCH Filed Jan. 27, 1967 I 2 Sheets-Sheet 2 James E. Shockroo, Manuel R.Lopes, Joseph L. McMorrow, aw/W8 M 7 Inventors:

United States Patent Office 3,470,513 THERMALLY-RESPONSIVE SWITCH James E. Shockroo, South Easton, Manuel R. Lopes,

Attleboro, and Joseph L. McMorrow, West Bridgewater, Mass, assignors to Texas Instruments Incorporated, Dallas, Tex., a corporation of Delaware Filed Jan. 27, 1967, Ser. No. 612,264 Int. Cl. Htllh 61/00 US. Cl. 337-86 3 Claims ABSTRACT OF THE DISCLOSURE A thermally-responsive switch having six terminals provides inherent protection against abnormal conditions in either Y-connected or delta connected three-phase electrical motors including dual voltage motors. Three of the terminals are connected to respective fixed contacts in the switch through heater elements and three of the terminals are connected to respective movable contacts mounted on and electrically insulated from a thermallyresponsive snap-acting bimetallic disc. The movable contacts normally engage the fixed contacts for completing electrical circuits through respective phase windings of the motor, the disc being located to be thermally responsive to abnormal winding temperatures and to abnormal current through any heater element for disengaging the contacts to open the motor winding circuits.

Background of the invention At the present time, thermally-responsive switches are available for providing inherent protection for Y-connected, three-phase electrical motors. In these prior art switches, a composite, thermally-responsive snap acting disc mounts movable electrical contacts which are electrically connected to the disc, the disc serving as the common or neutral point in the Y-connected motor circuit. When abnormal conditions in such a motor result in excessive current passing through any motor winding or in excessive winding temperature, the thermally responsive member is adapted to move for opening the winding circuits. However, where delta-connected motors are employed, such prior art protectors cannot be used. For protecting deltaconnected motors, separate overload protectors responsive to abnormally high currents in the motor windings are conventionally installed in the respective winding circuits at locations remote from the windings. In addition, separate thermostat means responsive to winding temperatures are located in close proximity to each of the motor windings, the overload protectors and thermostats cooperating to open a relay and to maintain the relay in open condition for deenergizing the motor windings during the occurrence of abnormal motor conditions. Because protection for delta-cotnnected motors has been so cumbersome and expensive, the protection has sometimes been omitted with attendant risks particularly where the motor is delta-connected after having been originally supplied for use in a Y-connected arrangement. This situation frequently arises in the case of dual voltage motors where the motors are generally Y-connected at the higher voltage but are often delta-connected at the lower voltage.

Summary of the invention In the switch or switch mechanism of this invention, three electrically conductive terminals are mounted in spaced relation to each other on an electrically insulating base or housing. These terminals are each connected through conventional heater elements to respective fixed electrical contacts mounted in spaced relation to each other on the insulating base. An additional three electrical terminals are connected to respective movable electrical 3,470,513 Patented Sept. 30, 1969 contacts, these movable contacts being mounted on and electrically insulated from a thermally-responsive snapacting composite disc or member. In a preferred construction, the thermally-responsive disc is mounted on the switch base and is normally disposed in a concavo-convex or dome-like shape, the disc including a layer of material of high thermal expansion characteristics which is bonded to a layer of material of relatively lower thermal expansion characteristics so that lower expansion material is on the convex side of the disc. The disc is normally located so that the movable contacts mounted thereon are engaged with respective fixed contacts in the switch but is adapted to move into convexo-concave shape with a snap-action in response to a selected rise in ambient temperature for disengaging the movable contacts from the fixed contacts.

In a preferred construction, each of the three movable contact means comprises a rivet or pin which extends through a plastic insulating bushing or the like extending through an aperture located near the rim of the thermallyresponsive disc. The head of the rivet abuts a flange of the bushing which rests against one side of the disc and, at its opposite end the rivet or pin extends through a plastic insulating washer or the like. The opposite end of the rivet or pin is peened, enlarged or capped with a relatively larger metal member so that the rivet or pin end rests against the plastic washer for holding the washer locked against the opposite side of the thermally responsive disc. In this arrangement, the head of each rivet or pin serves as a movable electrical contact adapted to engage one of the fixed contacts and the opposite end of the pin is preferably connected to a flexible, electrically conductive lead or pigtail which either serves as an additional switch terminal or is electrically connected to a switch terminal. Of course, the heater elements connected to the fixed switch contacts are located with respect to the thermally responsive disc so that the disc is adapted to be responsive to heat generated by the heater elements.

The thermally-responsive switch of this invention is adapted to be mounted within the housing of a threephase electrical motor so that the disc is directly responsive to heat generated by the motor windings, thereby to provide the desired inherent protection for the motor. Where the motor is Y-connected the motor windings are connected at one end to respective line leads and at their opposite ends to the respective switch terminals which are connected through the heater elements to the three fixed electrical contacts. The other three switch terminals are then connected together to form the common or neutral point in the power circuit for completing the Y-connection of the motor. In this arrangement, each motor winding is normally connected at one end to a line lead and at the opposite end through a switch terminal, a heater element, a fixed contact, a movable contact and a second or additional switch terminal to the neutral point in the power circuit. In this way, the thermally responsive disc is responsive to abnormally high current through any heater element or to abnormally high winding temperature for opening the circuits through all motor windings.

Where the motor is delta-connected, the three switch terminals, which are connected at one end to the fixed electrical contacts through the heater elements, are connected at their opposite ends to respective line leads. Each common point between the connected pairs of the motor windings is then connected through one of the additional switch terminals to a movable switch contact. In this arrangement, each line lead is normally connected to a switch terminal, a heater element, a fixed switch contact, a movable switch contact and an additional switch terminal to a common point between a pair of motor windings. In this way, the thermally responsive disc of the switch is responsive to abnormally high current through any heater element or to abnormally high winding temperature for opening the circuits through all motor windings.

Objects, advantages and details of the switch provided by this invention appear in the following description of preferred embodiments of the invention, the description referring to the drawings.

Brief description of the drawing FIG. 1 is a plan view of the switch provided by this invention;

FIG. 2 is a plan view similar to FIG. 1 showing the switch with the thermally-responsive member thereof received;

FIG. 3 is a section view along line 33 of FIG. 1;

FIG. 4 is a partial section view to enlarged scale along line 44 of FIG. 1;

FIG. 5 is a perspective view to enlarged scale illustrating terminal and contact means of the switch of FIG. 1;

FIG. 6 is a partial section view similar to FIG. 3 illustrating an alternative embodiment of the invention;

FIG. 7 is a partial section view similar to FIG. 3 illustrating another alternative embodiment of the invention;

FIG. 8 is a schematic view illustrating use of the switch of this invention for protecting a Y-connected three-phase electrical motor;

FIG. 9 is a schematic view illustrating use of the switch of this invention for protecting a delta-connected three-phase electrical motor; and

FIG. 10 is a perspective view of a connector means for use with the switch of this invention.

Referring to the drawings, 10 in FIGS. 1-3 indicates the novel and improved thermally-responsive switch of this invention. As shown, the switch includes a base or housing means 12, preferably formed of a conventional, molded, electrically-insulating phenolic resin or the like. The base is preferably of a hollow cylindrical shape closed at one end 14 and has a threaded bushing portion 16 centrally located within the base. Three electrically conductive terminals 18 are fitted securely into openings 20 in the base end 14 and are provided with hook-like end portions 19 to which electrical connections are easily made outside the base. The opposite ends 21 of the terminals 18 are bent to rest upon shoulders 22 molded within and spaced equally around the base 12.

Inside the base, three fixed electrically conductive contact means 24 are also tightly fitted in openings 26 in the base and are bent at their ends 27 to rest upon shoulders 28 molded within and spaced equally around the base.

Conventional heater elements 30, each preferably formed of a coil of resistance wire of conventional heater material are welded or otherwise electrically connected at one end 31 to a respective terminal 18 and at an opposite end 32 to a respective fixed contact means 24 as is shown in FIGS. 1-3. See also FIG. 5.

A threaded stud 33 having one end 34 with fiat surfaces which can be gripped by a wrench or other tool is threadedly engaged at one end in the bushing portion 16 of the base so that the end 34 of the stud can be gripped from outside the base. The stud 33 has a shoulder 35 located near its opposite end and a snap-acting composite thermostat or thermally-responsive member 36 is mounted on the stud. That is, the thermally-responsive member 36 has a central aperture 38 which fits loosely around the stud so that the member 36 rests on the stud shoulder 35, the stud having an enlarged head 40 welded or otherwise formed on the stud for locking the member 36 on the stud without restricting rotation of the stud relative to the member 36. The thermally-responsive member has three extending peripheral portions 42 4 7 equally spaced around the perimeter of the member which fit between ribs 44 molded in the base 12 so that the ribs prevent rotation of the member 36 during rotation of the stud 33.

The thermally-responsive member 36 preferably comprises a dome-shaped, concavo-convex bimetallic snapacting metal disc such as is shown in Spencer Patent No. 1,448,240. Such a member preferably comprises two layers 36.1 and 36.2 of metallic material of high and relatively lower thermal expansion characteristics bonded together in composite form with the material of lower expansion characteristics 36.2 located on the convex side of the member. As will be understood, such a member is adapted to respond to a selected increase in the ambient temperature to move with a snap-action into convexoconcave shape as its position of opposite concavity can be called.

In accordance with this invention, three movable contact means 46 are mounted on and are electrically insulated from the thermally-responsive member 36. For example, each of the extending portions 42 of the member 36 has an aperture 48 through which a bushing 50 flanged as at 52 is fitted as shown in FIG. 4. A washer 54 is then aligned with each of the apertures 48 and an electrically conductive rivet 56 is fitted through the bushing and washer, the rivet head 58 and an enlarged 1 end or cap 60 formed on the rivet cooperating to hold the bushing flange 52 and the washer 54 securely locked against the sides of the thermally-responsive member. The bushing 50 and washer 54 are formed of plastic, electrically-insulating material such as the fluorocarbon commonly designated Teflon for electrically insulating the rivet 56 and its head and cap from the member 36. As will be understood, the rivets comprise the movable contact means 46, the rivet heads being adapted to engage the fixed contact means 24 and the rivet caps being adapted to serve as or to be electrically connected to additional terminal means. As will be understood, the stud 33 is rotatable for drawing the movable contact means 46 against respective fixed contact means 24 with a selected force or pressure.

In the preferred embodiment of this invention, conventional flexible wire leads or pigtails 62 are brazed or welded or otherwise electrically connected to the movable contact means 46 and extend through apertures 64 in a cover 66 cemented on the base means 12 as illustrated in FIG. 6. In this construction, the pigtails themselves serve as additional terminals to which electrical connections can be made outside the switch 10. However, in an alternate construction illustrated in FIG. 7, three other additional terminals 68 are mounted on the base cover 66 by means of tubular rivets 76 and the pigtail leads 62 are brazed, welded or otherwise electrically connected to the respective additional terminals 68. As shown in FIG. 7, the pigtail leads 62 are preferably of suflicient length so that they extend slackly between the movable contact means 46 and the other additional terminals 68 and thereby avoid any restriction of the movement of the member 36 in response to changes in ambient temperature.

In this construction, the switch 10 is adapted to be associated with a Y-connected three-phase electrical motor as is schematically illustrated in FIG. 8 for providing inherent protection for the motor. That is, the three-phase windings 72, 74, 76 of a three-phase electrical motor 77 are electrically connected at one end to the respective line leads 78, 80, 8-2 of a conventional power source. The windings are then electrically connected at their other ends by brazing or the like to respective terminals 18. In the embodiment of the switch 10 illustrated in FIG. 6, the three pigtail leads 62 are then electrically connected together as at 83 by brazing or the like to serve as the common or neutral point of the Y-connected motor circuit. The switch 10 is preferably mounted within the housing (not shown) of the motor 77 to be in relatively close heat-exchanging relationship to the motor windings as will be understood. In this arrangement, each motor winding is connected at one end to a line lead 78, 80 or 82 and at its other end, through a terminal 18-, a heater 30, a fixed contact 24, a movable contact 46 and a pigtail 62 to a common or neutral point of the motor circuit. The heater elements are disposed as illustrated in FIGS. 1-3 in heat-exchanging relationship to the thermally-responsive member 36. Upon the occurrence of an abnormal motor condition of any sort resulting in heating of any motor winding or in passing of excessive current through any motorwinding, heat generated by the winding and by the heater element 30 cause a rise in the ambient temperature to which the thermally responsive member 36 is exposed, thereby causing the member to move to its position of opposite concavity for simultaneously opening all of theimotor winding circuits.

Alternatively, the switch is also adapted to be associated witht a delta-connected three-phase electrical motor as is schematically illustrated in FIG. 9 for .providing inherent protection for that motor. That is, pairs of the three-phase windings 84, 86 and 88 of the motor 90 are electrically interconnected as shown in FIG. 9 and the common points 92, 94 and 96 between the pairs of windings are electrically connected by brazing, welding or the like to the respective pigtail leads 62. The switch terminals 18 are then electrically connected by brazing, welding or the like to the respective line leads 98, 100 and 102 of a conventional power source. The switch 10 is preferably mounted within the housing (not shown) of the motor 90' to be in relatively close heat-exchanging relationship to the motor windings as will be understood. In this arrangement, each common point 92, 94 and 96 of the motor windings is connected through a pigtail lead 62, a movable contact means 46, a fixed contact means 24, a heater element 90 and a terminal 18 to a respective line lead 98, 100 or 102 of the power source. Upon the occurrence of an abnormal motor condition of any sort resulting in heating of any motor winding or in passing of excessive current through any motor winding, heat generated by the winding and by a heater element 30 cause a rise in the ambient temperature to which the thermally-responsive member 36 is exposed, thereby causing the member to move to its position of opposite concavity for simultaneously opening all of the motor winding circuits.

When the switch embodiment illustrated in FIG. 7 is used for protecting a Y-connected three-phase electrical motor, the connector 104 shown in FIG. 10 is preferably used. As illustrated, the connector 104 incorporates a lead 106 electrically connected by brazing or the like to three conventional terminal means 108 which have bifurcated spring-like leaves 110 for detachable attachment of the connector 104 to the switch terminals 68. Although particular embodiments of the switch of this invention have been described by way of illustration, this invention includes all modifications and equivalents thereof falling within the scope of the appended claims.

We claim:

1. A thermally-responsive switch for the protection of Y-connected or delta-connected three-phase electrical motors comprising insulating base means, three terminal means fixedly mounted at one end of said base means, three fixed electrical contact means mounted on said base means, three electrical heater means electrically connecting said fixed terminal means to respective fixed contact means, a thermally-responsive disc having a selected dome-shape at a first temperature, said disc being adapted to move to an inverted dome-shape in response to a selected change in temperature, three movable electrical contact means mounted on said thermally-responsive disc, said movable contact means each being electrically insulated from said disc and extending through said disc, said thermally-responsive disc being mounted on said base means in heat exchange relation to said heaters for holding a portion of each of said movable contact means at one side of said disc in engagement with said respective fixed contact means at said first temperature and for moving in response to said selected change in temperature for disengaging said portions of said movable contact means from said fixed contact means, and three flexible lead means respectively attached to portions of said movable contact means at the opposite side of said disc to extend from said base means at a side of said base means opposite said fixed terminal means.

2. A thermally-responsive switch as set forth in claim 1 having three additional terminal means mounted on said base means at said opposite side of said base means, said additional terminal means being respectively attached to said flexible lead means, said flexible lead means being of sutficient length to slackly extend between said additional terminal means said movable contact means for avoiding restriction of movement of said thermallyresponsive disc.

3. A thermally responsive switch as set forth in claim 1 adapted for protecting a Y-connected three-phase electrical motor, said switch further comprising three electrically-interconnected terminal means detachably attached to said respective additional terminal means.

References Cited UNITED STATES PATENTS 2,651,696 9/1953 Seely 337-86 1,664,201 3/1928 Fay 337-89 BERNARD A. GILHEANY, Primary Examiner DEWITT M. MORGAN, Assistant Examiner US. Cl. X.R. 337-89, 102 

